Pipe organ simulation circuits



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PIPE ORGAN SIMULATION CIRCUITS Filed March 27, 196?- 5 Sheets-Sheet Z Q Q O I I INVENTORS I I g I 0,4/v/EL N Mwr/N ,4 EXANOEE 5. EEPESK/N ATTORNEYS y 0, 1967 o. w. MARTIN ETAL 3,322,874

' PIPE ORGAN SIMULATION CIRCUITS Filed March 27, 1962 v 5 Sheets-Sheet 4 an/v/a l4. Amer/N ,4: 964N059 5. EEQESK/N ATTORNEYS INVENTORS A May 30, 1967 Filed March 27, 1962 COMPLE X coNTmuous KEY D. W. MARTIN ETAL PIPE ORGAN SIMULATION CIRCUITS 5 Sheets-Sheet 5 GENERATORS SWITCHES an i HF! v r /g Aw A 313 wxan 300 3 4, LF L HFr--- 5 30\ 305 LF HLTER HF|-------- I A azl M L. 02 306 LF 7 Q A P me M 7 L KEY L SWITCHES am TONE DELAY 300/ GEN. c

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TONE Gm T DELAY 30 301 INVENTORS,

ATTORNEYS United States Patent .0

3,322,874 PIPE ORGAN SIMULATION CIRCUITS Daniel W. Martin and Alexander B. Bereskin, Cincinnati,

Ohio, assignors to D. H. Baldwin Company, a corporation of Ohio Filed Mar. 27, 1962, Ser. No. 182,788 20 Claims. (Cl. 841.13)'

The present invention relates generally to electronic organs, and more particularly to audio systems for elec-- tronic organs, having provision for introducing envelope build-up delay in the pedal division output of the electronic organ, on a frequency selective basis, to simulate the tonal build-up pattern ofa pipe organ.

In a pipe organ the pipes of very lowest fundamental frequency of the pedal division of the organ, havea much longer build-up time than do the pipes of higher fundamental frequency, and as a rough approximation, total build-up time decreases as a' direct function of fundamental frequency. However within the complex spectrum of a single pipe tone the partials of lowest frequency build up more slowly than the highest partials, so that the timbre of the tone changes during tonal buildup from a thinner to a rounder or more mellow tone color. Build up at any one frequency is approximately logarithmic as a function of time. It isconsidered musically desirable by the classical organist that the acoustic output of the electronic organ simulate that of the pipe organ in every respect. In particular, the pipe organ provides certain transient sound variations which are considered .to be characteristic of such organs, and among such ent build-up time for each'channel. By suitably selecting build-up delay characteristics'for the several channels, as well as the frequency limits of the several'channels, an appropriate over-all tone-envelope build-up characteristic, for the entire pedaldivision, can be attained. The separation of'separate sub-bands into separate physical channels also facilitates use of amplifiers and radiators which have optimum. characteristics for the frequency ranges involvedv More particularly, a relatively lower power amplifier is adequate for higher frequencies than for lower frequencies, and a low frequency speaker or other radiator can be most effective if it need not have capacity for radiating'high frequencies. The use of'separate high and low frequency speakers, supplied with driving current through a frequency dividing or cross-over network, is commonplace in the audio art. Butuse of this expedient has not heretofore been taken advantage of tothe division point are not delayed or aredelayed only slightly. The frequency division point which provide optimum simulation of pipe organ tone build up. is not necessarily, however, the samefrequency which permits opti mum amplification and radiationofsound viatwo loudspeakers, on a frequency division' basis. The tones of large organs can extend down'to' about16c.'p.'s., i.e. into the infrasonic range. A loudspeaker or sound radiator which is capable of effective operationat 16 c.p.s; cannot be expected to operate effectively at'very high fre quencies, whereas an audio-frequency loudspeaker having capability down to 32 c.p.s. is conventional. Accordingly, we provide a division or cross-over point for sound radiation, as distinct from build-up, at about 30 c.p.s., but introduce delayed build up of tones, above and below the'200 c.p.s. division point which are appropriate to the latter division point. According to this embodiment of the invention the tonal output of an electronic organ is separated into two channels, With frequency division at 200 c.p.s. The low-frequency channel is caused to build up to maximum output slowly, and the high-frequency chan nel rapidly. The outputs of the channels are combined, and then re-divided, with frequency division occurring at 30 c.p.s. for purpose of radiation through an infrasonic loudspeaker and a normal audio-frequency loudspeaker.

As an alternative, and'especially inorgans having a 32' foot stop which is primarily fundamental, all sound originating in tone generators below about 30 c.p.s. may be directly applied to a low-frequency channel, having an infrasonic speaker and provision for separate delayed I buildup. The remaining tone generator outputs may be connected to a second channel, having an audio-frequency speaker, but also containing provision for division into' sub-bands at a 200 c.p.s. division point. The frequency components below' about 200c.p.s. may be subject todelayed build-up before being connected to the audio-frequency amplifier and loudspeaker, while those above are not. The last described embodiment, involving division on' the basis of tone generators, has the feature that the fundamentals of the infrasonic tones' are delayed together with their associated harmonics, which is nottrue where division is accomplished" solely on a frequency'basis. It

also has the advantage that very little audio-frequency energy is required from the amplification'and radiation equipment designed for the infrasonic range. It has the further advantage of facilitating employment of three different build-up times, one for the infrasonic range, another for the audio range to 200 c.p.s. and the third for the audio range above 200c.p.s'. The latter delay may be zero, if desired.

The 200 c.p.s. division point, below which delayed buildup occurs, is an arbitrary division point; Experience has indicated that frequency division points of over 500 c.p.s.

may well be introduced, provided that appropriately shorter delay envelopes are utilized.

Circuitry for developing delayed-gain in an infrasonicfrequency keyed channel, without introducing distortion and key thumps, is provided interms of a balanced diode bridge. Delayed buildup occurs in response to control signals derived from thevery tones in which delayed buildup is desired. Immediately on initiation of a tone by depression of a pedal, development of a pair of oppositely poled control voltages is started, one in response to positive excursions or half cycles of the toneand the other in response to negative excursions or half cycles. The tone which is to be delayed in buildup is-applied to the input of an amplifier through a balanced diode bridge, which normally, i.e. in the absence of control signal, blocks the tone, and which is'rendered gradually conductive in response to action of the separate control voltages upon the opposite halves of the bridge. Because the control voltages are applied to conjugate terminals of the bridge, they oppose and balance out at-the amplifier input. The diode bridge thus acts as a variable voltage-responsive seriesattenuator', in which attenuation for zero" an electronicorgan is utilized to develop two control voltage waves which rise quasi-logarithmically or logarithmically from zero to a predetermined level, at a rate appropriate to tonal build up in pipe organs, in opposite polarities. These are generated by means of transistorized gating circuits, instead of by means of diodes. The control voltage waves are utilized to vary the attenuation in the low frequency channel of a frequency divider network by varying the shunt impedance presented by a diode bridge, rather than by varying series impedance. The two outputs of the crossover network, i.e., high and low frequen-cy ranges, but with the low frequency range having been subjected to envelope delay, are then recombined to provide the total tone. The modification described in the present paragraph is suitable for utilization in substitution for the system previously described.

While the present brief description of the invention pertains to the pedal division particularly, the utility of the system is not restricted to the pedal division. Very low frequency tone can occur in any division of the electronic organ, and in respect to such tones appropriate envelope shapes to simulate pipe organ tonal build up effects are desirable. However, where the build up occurs in a single circuit for an entire division, it is not desirable to incorporate the required circuitry in other than the pedal division, because of the complexity of music in the other division. It is usual, in the pedal division, to play one note at a time, but not in the other divisions. Also, notes are often played slowly enough, in the pedal division, to afford time for the required build up and decay, whereas in the remaining divisions key manipulation is often extremely rapid.

In order to render the invention applicable generally to the electronic organ, i.e. to all divisions, and to enhance the advantages of the system as applied to the pedal division, it is necessary to provide a separate envelope buildup circuit for each tone generator. In the pipe organ, tonal build up of a complex tone takes place at a different rate for the higher partials than for the fundamental. Accordingly, for each tone generator we provide a frequency divider network which separates the lower harmonics from the higher harmonics, and we delay the lower harmonics, thereafter recombining the tonal components. In more elaborate systems different partials of a simple note might be separated into separate channels, each partial subjected to an appropriate delayed build up, and the partials thereafter recombined to form the complete note. Only economic considerations limit the possibilities in these respects. The advantages of treating each tone generator individually is that the playing of one note does not in hibit the build up of any other note, as is the case in FIGURES 1-3, for example, and, in fact, where each partial of each tone is individually treated in respect to delayed build-up, the pipe organ action is most nearly simulated.

A simplified form of pipe organ simulation can be attained by introducing delayed build up entirely on a tone generator basis, without distinction of partials. Such a system fails to fully simulate the action of a pipe organ, in which delay for separate partials is different, but requires no frequency division or recombining networks, and hence is economically desirable.

It is, accordingly, a broad object of the invention to provide an electronic system for simulating the tonal build up, as a function of time, of the tones of a pipe organ.

It is another object of the invention to provide a system for differentially delaying build up of different frequency sub-bands of the tonal output of an electronic organ.

It is still a further object of the invention to provide a novel balanced keying circuit for alternating current signals, which employs a diode bridge.

It is a further object of the invention to provide circuitry for dividing a relatively wide band of frequencies into two sub-bands, delaying the build up of the lower frequency sub-band, and recombining the sub-bands, without introducing subjectively unpleasant distortion.

It is a further object of the invention to provide a system for delaying build-up of only the infrasonic com ponents of organ music approximately logarithmically and with a total delay time of about 2 seconds.

It is another object of the invention to provide an integrating circuit for generating predetermined approximately logarithmically increasing wave forms of opposite polarities and substantially equal amplitudes With respect to ground, and a predetermined maximum peak-to-peak level.

A further object of the invention resides in the provision of circuitry for integrating opposed half cycles of a signal to generate two equal gradually increasing control voltages of opposed polarities.

It is still a further object of the invention to provide an electronic organ which simulates a pipe organ in its tonal envelope build up characteristics, wherein each tone generator is individually treated in respect to build up delay.

Still a further object of the invention is to provide an electronic organ which simulates a pipe organ in its tonal envelope build up characteristics, wherein individual partials of each tone are individually treated in respect to built up delay.

The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a block diagram of a simplified tonal envelope build-up system for electronic organ, wherein differential delays are introduced on a frequency basis;

FIGURE 2 is a block diagram of a modification of the system of FIGURE 1;

FIGURE 3 is a block diagram of a modification of the system of FIGURE 2, wherein one of the build-up delays is applied on a fundamental frequency basis, rather than on an absolute frequency basis;

FIGURE 4 is a schematic circuit diagram of a system of division into low and high frequency components, delayed envelope build-up of low-frequency components, and reconstruction of low and high frequency components, which may be employed in various of the systems of FIGURES 1-3;

FIGURE 5 is a schematic circuit diagram of an alternative to the system of FIGURE 4;

FIGURE 6 is a block diagram of a tonal envelope build-up system, wherein tonal build-up occurs separately for each tone generator, and wherein partials of each tone are differently treated; and

FIGURE 7 is a block diagram of a modification of the system of FIGURE 6, wherein build-up delay for each tone generator is total for the tonal output, rather than different for different partials.

Referring now more particularly to the accompanying drawings, the reference numeral 10 represents the pedal division of an electronic organ which generates pedal tones including those in the infrasonic range, where the infrasonic range may be defined as falling below about 30 c.p.s. In general the lowest tone generated by organs is 16 c.p.s.

The output of the electronic organ division 10 is applied -in parallel to four band pass filters, identified by the reference numerals 11, 12, 13, and 14, having pass bands 16 to c.p.s., 100-400 c.p.s, 400 to 1600 c.p.s. and 1,600 to 20,000 c.p.s., respectively. Band pass frequencies utilized are in considerable degree arbitrary. The lowest frequency needed in any of the filters is 16 c.p.s. and the highest frequency about 20,000 c.p.s., but intermediate these points more than four filters, or less than four filters, may be utilized and basically the band pass ranges for the separate filters may be selected largely on the basis of economics and ease of electrical design. A desirable delay at 16 c.p.s. is about 2 seconds, i.e. it is desired that the 16 c.p.s. frequency build up logarithmically from zero at the time the appropriate pedal is depressed, to practically full volume, in about two seconds. Buildup time for higher frequency notes is smaller, and where a band pass filter is utilized to pass simultaneously a band of tones, so that these must all "be subjected to the same 'buildup delay, it is usually preferable to select a delay time which is shorter than that suitable for the lowest frequency and perhaps slightly longer than that suitable for the highest frequency. For example, in conjunction with the filters 11, 12, 13 and 14, respectively may be employed delay devices 15, 16, 17, 18 introducing delay times of 05 second, 0.25 second, 0.10 second, and 0.05 second, respectively. However, the highest frequency filter may have no delay if desired, and the remaining delay times may be considerably altered, on the basis of subjective tests, without departing from the spirit of the invention. The outputs of the filters 15 and 16 may be combined in a relatively highpower amplifier 19 and radiated through a low-frequency loudspeaker 20. The outputs of the filters 17 and 1'8 may similarly be applied to a lower power amplifier 21 and radiated through the relatively high-frequency loudspeaker 22.

The filters 11 to 14, then, provide frequency-range dividing networks which might in any event have been desirable in order to permit utilization of appropriate power amplifiers and loudspeaker designs. Generally, the lower frequencies require higher power and a relatively larger loudspeaker, whereas the higher frequencies require lower power and a relatively smaller loudspeaker. It is the usual practice in audio system design to provide appropriate frequency-range dividing network, amplifiers, and loudspeakers, but in the present case the availability of the networks and their cutoff frequencies may be selected to facilitate insertion of the desired buildup delays.

In the system of FIGURE 2, the pedal division of an electronic organ is represented by the dotted block 30, and contains therein, in addition to the usual tone generators, keying switches and the like, a series of tone color filters, 31, 32, 33, and 34. All of the tone color filters are connected to a common bust 35, via appropriate stop switches, the stop switches being identified by the reference numerals 36, 37, 38, and 39. The organ 30 further includes an expression control 40, followed by a frequency-range dividing network 41 having a division point at 200 c.p.s. The frequency division point is rather arbitrary, but should occur in the low audio frequencies, say below 600 c.p.s. The high-frequency range proceeds through a channel 42 to a linear mixer 43, while the low-frequency range proceeds through a channel 44 to a delayed-gain circuit 45, having a maximum gain of unity, to the same linear mixer 43. For the frequency division point suggested a delay time of about .3 to .5 second would be appropriate.

The output of the mixer 43 is applied to a further frequency-dividing network 46 having a division point at 30 c.p.s. The range below 30 c.p.s. emerges from the dividing network 46 through a channel 47 and proceeds to power amplifier 48 and infrasonic loudspeaker 49. The range above 30 c.p.s. proceeds through a separate channel 50 to an appropriate amplifier 51 and an audio-frequency loudspeaker 52.

In the case of the system of FIGURE 2 all frequency divisiontakes place on a frequency basis, and, in consequence, high harmonics ofa given tone may be subject to no delay, while low harmonics of the tone may be sub jectedto delay, or delays between low and high harmonics may differ.

While. in the system of FIGURE 2 frequency division takes place by means of filters, and therefore occurs on a frequency basis, in the system of FIGURE 3 frequency division takes place by, grouping tone generators. The difference in operation asbetween the systems of FIG- URES 2 and 3 is, that in the system of FIGURE 2 higher harmonics of an infrasonic tone may be treated differently in respect to delay build up than are the lower ones,

6 whereas in the system of FIGURE 3 all of the harmonics of any given infrasonic tone are treated. identically. In the system of FIGURE 3 the reference numeral 60 denotes the pedal division of an electronic organ having the usual tone generators, key switches, tone color filters and the like. Included in they organ 60 is an octave series of key switches 61a corresponding to the lowest octave in the pedal range, a filter 62 for tones in this infrasonic range, of 16-32 c.p.s., another series of key switches 61b, its tone color filter 63, and a series of filters 65, 66, 67 representing stop filters for all frequencies above the lowest octave in the pedal range. The output of the filters 63, 65, 66, 67, ie all those pertaining tofrequencies above the lowest octave of the pedal range, are gathered on a single bus 70, subjected to expression control at 71' and then applied to frequency divider network 72 having a division point selected at 200 c.p.s. Frequencies above 200 c.p.s. pass through the channel 73 directly to a linear mixer 74, whereas frequencies below 200 c.p.s. pass through the channel 75 to the mixer 74. The channel 75 includes a delayed buildup circuit 76 having a maximum delay time of about .3 to .5 second. The output of the mixer 74 is amplified in a power amplifier 77 and radiated by meansv of a conventional loudspeaker 78.

The output of the lowest octave filter 62, i.e. at 16-32 c.p.s., passes directly, without the interposition of anexpression. control, to a delayed gain circuit which may have a total delay time of as much as 2 seconds. The out put of the delayed-gain circuit 79 is applied .to a power amplifier 80 and the output of the latter is radiated by means of an infrasonic loudspeaker 81.

In FIGURE 4 is schematically illustrated a suitable circuit for accomplishing frequency division, delayed gain buildup and linear mixing, corresponding generally with the components 41 to 45 of FIGURE 2, or 72 to 76 of FIGURE 3. The delayed gain circuit 79 (FIGURE 3) may also include the circuitry of FIGURE 4, keeping. in mind that linear mixing is not requisite in the delayed.

gain circuit 79 of FIGURE 3.

In the system of FIGURE 4 the entire audio and infrasonic tonal output of the pedal division of an organ, as in FIGURE 2, or the entire pedal output exclusive of the lowest octave filter, as in the system ofFIGURE 3, may be applied to an input terminal 100. The terminal.

tube 104 through the condenser 107. The vacuum tube 111 is provided with a bias and negative feedback cathode resistance 112 and with an anode load 113. The anode of the vacuum tube 111 is coupled through a DC. blocking capacitor 114 and a voltage dropping resistance 11-5, to a control waveform generating circuit 116 which has the function of developing a control voltage wave which establishes the delayed-gain buildup. The control voltage generator 116 includes two channels, 117 and 118. Channel 117 includes a diode 119 having its anode presented to the vacuum tube 111, whereas, the channel 118 includes a diode of opposite polarity. Connected between the cathode of the diode 119-and the anode of the diode 120 is a Zener diode 121, shunted by a leakage resistance path. Because of the opposed polarities of the diodes 119 and 120, and further because of the DC. isolating con-- denser 114, the diode 119 passes only positive half cycles.

of any wave form applied thereto, and the diode 120 passes onlynegative half cycles of any wave form applied thereto. The Zener diode 121 acts to clip the peak-to-peak voltage provided by the diodes 119, 120, since the peakto-peak value cannot exceed the firing voltage of the Zener diode 121. Sufficient electrical gain is provided ahead of the clipper for the peaks of weakest tone waves to exceed the clipping threshold. Thus the control voltages, and the resulting tone buildup, will be independent of the magnitude of the organ signals, so the buildup effect occurs similarly at the beginning of any tone wave. Of course clipping could be accomplished by other means, e.g. in amplifier stage by overload, ahead of rectification.

Connected between the cathode of the diode 119 and ground is a low pass filter comprising shunt capacitors 122, 123, 124 and series resistances 125, 126. Connected between the anode of the diode and ground is a precisely similar low pass filter comprising capacitance 127, 128 and 129 and series resistances 130, 131. The low-pass filters are connected in a conventional configuration, and serve as integrating networks for the voltage pulses passed by the diodes 119, 120, and clipped by the Zener diode 121. At the output of the filters, i.e. on leads 140, 141 appear, then, gradually increasing voltages, with respect to ground, which increase for each cycle of tone applied to the diodes 119 and 120 respectively, until the peakvoltage appearing across the condensers 122 and 127, taken in sum, equals the firing voltage of the Zener diode 121. At this point the charging process is discontinued, because of back biases on diodes 119, 120, except in respect to replenishment of leakage from the storage capacitors of the filters.

The channel 102 leads to one half of a cross-over network 142, which serves to bypass in channel 102 all frequencies above some predetermined value, and to pass all frequencies below that value, which, taken in the species of the invention illustrated in FIGURES 2 and 3, may be 200 c.p.s. However, values up to 1000 c.p.s. may be utilized, if desired. The sub-band of frequencies passed by the filter 142 proceeds to a balanced diode bridge 143. The latter consists of four diodes, 144, 145, 146, 147. The diode 144 has its cathode connected to the filter 142 and its anode connected to the anode of the diode 145, which in turn has its cathode connected to the input circuit of an amplifier stage 150. The anode of the diode 147 is connected to the filter 142 and to the cathode of the diode 146, the anode of which is connected to the grid of the amplifier stage 150. It follows that the bridge circuit 143 is normally blocked, i.e. blocks passage of currents from resistor 151 to the amplifier stage 150, since each of the series paths through the diodes includes two diodes which are respectively of opposite polarities. The lead proceeds to the junction of the diodes 144, and the lead 141 to the junction of the diode 146, 147. The voltage applied to the lead 140 is positive with respect to ground and that on the lead 141 negative with respect to ground. Accordingly these voltages, acting as control voltages, unblock the blocking diodes of the bridge 143. The amplification provided by the amplifier stage 103 and 110, in conjunction with the clipping-circuit control-voltage generating circuit 116, are such that when full voltage is developed on leads 140, 141, i.e. at the end of an integration period, even for a weak input signal at the terminal 100, sufficient bias voltage is developed to render the bridge 143 fully conductive in both directions.

The channel 101 and amplifier 103 pass the entire frequency range of tones applied to the terminal 100, whereas the channel 102 passes only the low frequencies. The output of the amplifier 103 is applied through highpass filter 154, comprising capacitor 154a and resistances 154b, 154a to a linear mixer 152, which also receives the output of low-frequency amplifier through coupling circuit 153. The mixer 152 is a cathode loaded amplifier and supplies the combined output to a terminal 155 as well as to lead 156 which returns to a terminal 157, and reconstitutes the input band, as seen at terminal 100, except for the delayed build-up of the low frequencies.

The channel 154 serves then to eliminate from the input to the linear mixer 152 all the low frequencies which are passed by amplifier 150, with delayed buildup. The signals added by linear 152 then consist of highs only, on depression of a pedal key, and of the original input spectrum as seen at terminal 100, after buildup is complete. On the other hand, the channels 117, 118 must receive the entire spectrum present at terminal 100, to assure that delayed buildup of low frequencies will always occur.

After a pedal switch is closed, and delayed build-up of low frequency tones has been completed, it is necessary that opening of the switch be accompanied by discharge of integrator 116 in preparation for a further cycle of operation. In the circuit of FIGURE 4 a continuously operative discharge path for the integrator 116 exists through a circuit including the diode bridge 143. This discharge circuit is operative even while the integrator 116 is charging, and not alone after completion of a pedal note. However, charge of the integrator overbalances discharge, due to the relative time constants. The existence of the discharge circuit tends to distort somewhat the exponential character of the charging cycle, as does also the switching characteristics of Zener diode 121, and to render the charging characteristic only approximately exponential. Moreover, the charging characteristics are exponential only approximately because multiple energy storage circuits produce a charge and discharge characteristic representative of a higher order differential equation.

In the alternative system of FIGURE 5 the reference numeral denotes an input terminal for the entire output of the pedal division of an electronic organ. This output is amplified in a voltage gain amplifier 181, the output of the amplifier 181 being applied to an impedance matching transistor amplifier 182 connected in the emitter follower configuration. The output of the amplifier 182 is positive, and is developed across an emitter load resistance 183. The amplifier 182 operates without saturating, and its output is supplied through coupling condensers 184 and 184a to the base electrodes of a pair of collectorloaded, grounded-emitter transistor amplifiers 185 and 186. The amplifier 185 comprises a PNP type transistor having a resistance load 189 connected between its collector and a positive voltage bus 187. The base of the transistor 185 is connected through a relatively high resistance 188 to the bus 187, and the bias on the transistor is thus arranged to saturate the transistor completely, whereby the collector is essentially at ground potential, in the absence, of driving signal applied to the base.

The transistor amplifier 186 includes an NPN transistor having a grounded emitter, and having a collector load in the form of resistance 190 connected between the collector and a negative bus 191. The base of the transistor 186 is connected to the bus 191 through a relatively high resistance 192 which provides a bias sufiicient to drive the transistor 186 to saturation, so that its collector is, in the absence of driving signal, essentially at ground potential.

The signal developed across the emitter follower load 183 is an alternating current signal. Its positive excursions drive the transistor 185 out of the saturated condition into cut-off and thereby raise the voltage at the collector of the transistor 185. The negative excursions on the other hand drive the transistor 186 out of the saturated condition, and into cut-off, and thereby lower the voltage of the collector of the transistor 186, or increase its negative voltage with respect to ground. The collector of the transistor 185 is connected to an integrating network in the form of a low pass filter and the collector of the transistor 186 is connected to a similar integrating circuit in the form of a low pass filter. The filter 193 is provided with an output lead 195, and the filter 194 with an output I lead 196. On the output leads 195, 196 are developed re volts and minus 10 volts, so that the average approximate values of the control voltages on the leads 195, 196 are respectively plus '5 and minus volts, when peak clipping is occurring in transistors 185 and 186. The combined gain of stages 1 81 and 182 is so arranged that for all organ signals in the practical range of levels, clipping will occur in stages 185 and 186, so that build up to full gain Will occur.

The voltage developed on the output leads 1 95 and 196 is developed gradually, as the integrating circuits 193 and 194 charge up in response to successive half cycles of driving signal applied to the bases of the transistors 185 and 186. The delay time of the filters may be taken as equal to twice the time constant of the filters involved, i.e. the time required for the integrators to build up to approximately 90% of their peak value. In the present case this time may be approximately /2 to 1 second.

The bridge circuit 200 iscomposed of four diodes. The lead 195 is connected to one corner 201 of the bridge and sees the cathodes of diodes 203 and 204. The lead 196 is connected to the opposed corner 202 of the bridge 200 and sees the anodes of diodes 205' and 206. Since however the lead 195 is positive and the lead 196 negative, while signals are being processed, and zero at all other times, leads 195 and 196 see a relatively low impedance in the absence of input signal. Of the other two corners of. the bridge one corner 207 is grounded, and the remaining corner 208 serves as a variable shunt load. connection for a low-pass filter circuit 209. The low-frequency components passed by the filter circuit 209 are transferred through the diodes 204 and 205, which present a low impedance, for shunt by-pass to the output of the filter 209. The terminal 208'is also connected by a lead 210 tothe grid circuit of a triode amplifier section 211. As the voltage of the leads 195 and 196 increases with respect to g'ro und potential, the bias applied to the diodes 205, 206 and 203, 204 increases, rendering these diodes progressively less conductive to a signal applied from the filter 209, so that the bridge 200 acts as a variable attenuator having zero or very small impedance for zero control voltage, progressively increasing impedance for increasing control voltage. As the impedance of the bridge 200 increases, a greater and greater signal appears at the grid of the amplifier 211, since the bridge 200 acts as one arm of a voltage divider circuit, the other arm of w hich consists ofresistance 212- atthe output of the filter circuit 209. Since the charging rate of the integrator or low pass filter networks 193, 194 is approximately exponential, the envelope of the signal received by the amplifier 211 is likewise exponential, beginning with zero output and increasing as afunction of time, until the impedance of the bridge" 200 attains a stabilized value, after the transistors 186, 185 stabilize. After this time the output of the amplifier 211 as seen at terminal 213remains proportional only to the amplitude o fthe input signal as applied at the input terminal 180.

From the terminal 180 extends a lead 215, to a high pass filter 216, comprising series condensers 2'17 and resistance 21$,which extend to thegrid of a triode amplifier section 219. A variable resistance 220 extends from thegrid of the amplifier section 219 to ground, and permits adjustment of the high-frequency channel to that of the low-frequency channel. The output of. the amplifier 2 19. appears at. a terminal 221. Terminals 213 and 221 are connected together to a terminal 222, which is directly connected to the control grid of a triode amplifier section 223 The latter is connected in the cathode-follower configuration and its cathode load 224 is coupled to an outputterrninal 225. Triodes 211 and 219 have a common cathode bias, circuit 230.

Connectedbetweenlhe terminal 222 and ground is. a

variableresistance226 whichenables one, by adjustment of itsresistance value, to adjust the overall gain of the system to unity.

Describing now briefly the operation of the system of 10 FIGURE 5', wide-band signals applied to the terminal 180, and deriving from the pedal division of an electronic organ, are amplified in amplifier 181 and the output of the latter is applied to an impedance transforming transistor stage 182. The latter stage drives a pair of peakclipping amplifiers of opposite polarity, one of which clips positive halves of the signal input wave, and the other which clips the negative halves. At the output of the clipping stages 185, 186, are connected integrating circuits 193, 194, which are designed to provide roughly exponentially rising outputs with respect to ground, one of the outputs rising positively and the other rising negatively. These outputs constitute control waveforms for a diode bridge 200 which operates as a shunt as one arm of a voltage dividing network, having very low impedance for zero control voltage. The low-frequency components of the total signal applied to the terminal are selected by means of filter 209, which is connected in series with the fixed resistance arm and the variable impedance of the bridge 200. The junction of the resistance 212 and the bridge 200 is connected to the input of an amplifier stage 211, which transmits the low-frequency com ponents, after these have been subjected by the bridge to envelope delay, to a linear mixer amplifier 223. The high-frequency components of the signal present on the input terminal 180 are selected by means of filter 216, for application incontrolled amplitude, and Without gain delay, to the input of. an amplifier 219. The output of the amplifier 219 is also applied to the mixer 223, so that all the original-frequency components may be reconstituted at the output terminal 225, it being rec alledthat the low-frequency signals, but not the highfrequency signals, have been subjected to envelope delay.

The systems of FIGURES 1 to'S, inclusive, do not completely simulate, in respect to tonal envelope build-up, the tonal characteristics of a pipe organ unless single notes are applied in sequence to the delay build-up circuitry. In the case of the pedal division of the organ, this will generally prove to be true, because the pedal division is commonly played by depressing one pedal at a time, at

least for the major portion of the total playing time. Insofar as one note is played immediately after the termination of another, the build up circuits will not have time to decay to quiescent condition, and accordingly the second of the notes will not start at zero amplitude, as it should. Where the second note is initiatedduring the playing of a first tone, the secondtone will not be subjected to any amplitude delay. However the systems of FIG- URES 1 to 5 are justified on an economic basis, as applied to the pedestaldivision of anorgan, because they operate well for the major portion of playing time of the pedal division. Furthermore the lack of gradual buildup in a second tone is hardly audible while a first tone is being sustained. Where it is desirable to simulate more closely the actual operation of apipe organ, asfor example by playing the low-frequency tones in the manual divisions, or even where tones in the pedal division are played very rapidly by a highly skilledorganist, one can apply the techniques of FIGURES 1 to 5 individually to each tone generator of the organ which is sufficiently low in frequency to require gain delay. In applying the techniques of the present invention to individual tone generators it is again desirable to treat differently the lower partials and the higher partials, because in a pipe organ the lower partials have longer build-up times than the higher partials of the same tone. In the ultimate each partialof the tone might be treated to introduce the build up time appropriate for that partial by empirical comparison with the output of apipe organ but, in practice, this may not be economically feasible. Accordingly the practice is followed of dividing eachtone into lower and higher harmonics, introducing the delay into the lower harmonics and little or no delay into the higher harmonics, recombiningithe delayed with the undelayed partials, and

utilizing the electrical tone so processed for producing the acoustically radiated tone of the organ.

Turning now more specifically to FIGURE 6 of the accompanying drawings, the reference numerals 300, 301, 302, 303 represent typical tone generators which may or may not pertain exclusively to the pedal section of electronic organ, but which do pertain to low-frequency tones for which simulation of pipe organ tone build-up is pertinent. The generators 300 to 303, inclusive, may pertain to the musical nomenclatures C, Cit, D, Dlt, and by extension all tone generators for one or more octaves may be subjected to the same treatment. In series with the generators 300 to 303, inclusive, are provided key switches 304, 305, 306, 307, respectively. Treating the key switch 304 as typical of the remainder of the key switches, i.e., connected in cascade with a frequency-range dividing network 310, it separates the low-frequency components of the tone applied thereto in a channel 311 and the remainder of the frequency spectrum of the generator 200 in a channel 312. In the channel 311 is included a gain delay network 313, which may utilize the circuitry of FIGURE 4 or 5 for introducing a controlled delayed build-up of the envelope of the tonal components applied to the gain delay device 313. The output of the delay device 313 and of the undelayed channel 312 are applied to a linear mixer 314, which is designed, as in the system of FIG- URE 5, to reconstitute the low-frequency and high-frequency components in their original relative intensities. The output of the mixer 314 is then applied to a conventional tone filter 315, power amplifier 316 and loudspeaker 317, in cascade. The tone generators 301, 302 and 303 are provided with frequency division, low-frequency tonal envelope build-up delay devices, each of which is individual to a tone generator, and which are individually identified by the reference numerals 320, 321, and 322. Further tone generators, corresponding with different musical nomenclatures, or the same nomenclatures in higher octaves, may be provided with similar circuitry. All the delayed and undelayed channels are connected to the same mixer 314, for combination with the tones generated by the generator 300.

The system of FIGURE 6 enables different build-up times to be applied to the lower and the upper partials of each tone on an individual basis. Upon depression of any pedal, or closure of any key switch, the upper partials of the corresponding tone are sounded immediately, but the fundamental of the tone or the lower partials build up gradually from zero value to a predetermined maximum value over a period of time appropriate for simulation of pipe organ tones.

In the system of FIGURE 6 considerable expense is involved in providing for each tone generator a frequency division network and controlled delay device. A rough approximation to the results obtainable by the system of FIGURE 6 may be attained much more simply and economically, although at considerable loss in performance characteristics, by omitting the frequency division networks and substituting in each of the tone generator channels merely a simple delay device. Thereby the partials, as Well as the fundamental, are delayed correspondingly, a mode of operation which is in fact foreign to the pipe organ.

In the systems of FIGURES 6 and 7, identical components or elements are identified by the same reference numerals. The system of FIGURE 7 requires no further explanation, since it duplicates the system of FIGURE 6, except for omission of frequency range division and recombination.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. A system for simulating pipe organ tones electronically, which includes a plurality of band pass filters, each passing a different sub-band of frequencies, a pedal division of an electronic organ connected to all said band pass filters in parallel, means for relatively delaying the build up of the lowermost sub-band of frequencies approximately exponentially for a total time of about .5 to 2 seconds with respect to the build-up of at least one other sub-band, wherein said lowermost sub-band is infrasonic.

2. A system for reproducing pedal tones of an electronic organ, comprising a pair of parallel signal channels of higher and lower frequency ranges, means for apply ing all said tones to a control channel, means responsive to signal in said control channel for generating positive and negative gradually increasing control voltage wave forms having a predetermined maximum peak to peak value, means responsive to said wave forms for controlling the envelope of the tones in the lower range one of said pair of channels and means for linearly combining the tones in the higher one of said pair of channels with the tones of controlled envelopes in the said lower frequency one of said channels.

3. An output system for low-range tone signals from an electronic organ comprising:

(a) a frequency dividing network receiving said signals and having at least two output points supplying components of said signals in different frequency ranges,

(b) at least two signal channels respectively connected to said output points, and

(c) delayed-gain means connected in at least the lower-frequency channel, whereby lower frequency components of said signals build up in amplitude at a slower rate than higher-frequency components of said signals, and

(d) output means operatively associated with said channels for converting said signal components to sound.

4. The combination claimed in claim 3, wherein said output means comprises (a) a mixer coupled to said channels, and

(b) amplification and loudspeaker means coupled to said mixer.

5. The combination claimed in claim 3, including a second output path for certain other signals in said electronic organ comprising (a) further delayed-gain means receiving said other signals,

(b) a power amplifier coupled to said further delayedgain means, and

(c) infrasonic loudspeaker means coupled to said power amplifier.

6. In a system for simulating pipe organ tonal build up in an electronic organ, a series of pedal tone generators, a key switch operatively associated with each of said pedal tone generators, a separate electronic tonal build up delay circuit operatively associated with each of said key switches, said electronic tonal build up delay circuits each arranged to introduce a tonal delay envelope commencing at zero on closure of a key switch and building up approximately exponentially to a predetermined amplitude-stabilized level in a time appropriate to simulate build up of pedal tone in an organ pipe, and means for acoustically radiating said tones including the build-up delay.

7. The combination according to claim 6 wherein each of said tonal build up delay circuits includes a frequency range division network, and wherein each of said tone generators is arranged to generate lower and upper partials, said frequency range division network being arranged to separate said upper and lower partials into separate channels, containing greater delay in the channel containing said lower partials and smaller delay including zero in the channel containing said higher partials.

8. The method of simulating pipe organ tones electronically, which includes the steps of: keying the electrical output of audio-frequency signal generators, applying the keyed signals to the inputs of both a control circuit and a variable amplification circuit, deriving from the control circuit a resulting control voltage gradually changing in time to a new fixed value, applying the control voltage to the variable amplification circuit to increase its gain gradually to a new fixed value, thus simulating the delayed build up of tones from organ pipes.

9. In combination, in an electric organ having a pedal division, a plurality of filters connected in parallel to said organ division, said filters each passing at least largely a different sub-band of the frequency band generated by said pedal division, a separate exponential delay circuit in cascade with each of said filters, the delay times of said delay circuits being approximately inversely functionally related to the mean frequencies of the associated filters, and means for acoustically radiating the outputs of said filters.

10. The combination according to claim 9 wherein said last means comprises plural power amplifiers and radiators, said power amplifiers and radiators being connected to diverse ones of said filters and having diverse power handling capabilities.

11. The combination according to claim 9 wherein said sub-bands extend approximately as follows: (a) 16 c.p.s. to 100 c.p.s. (b) 100 c.p.s. to 400 c.p.s. (c) 400 c.p.s. to 1600 c.p.s. (d) 100 c.ps. to 20,000 c.p.s. and the associated delay times are approximately (a) 0.5 sec. (b) 0.25 sec. (c) 0.10 sec. (d) 0.05 sec.

12. A system for simulating pipe organ tones by means of an electric organ, comprising a division of said electric organ, means connected to said division for dividing its tonal output into separate channels on a frequency division basis, means for introducing exponential build-up of tone into at least one of said channels, build-up time being in accordance with the build-up time of corresponding frequencies of said pipe organ, and acoustic radiating means connected to said channels and arranged to radiate into a common acoustic space.

13. The combination according to claim 12 wherein said division is the pedal division.

14. The combination according to claim 13 wherein said channels number two.

15. The combination according to claim 13 wherein said channels number more than two.

16. A system for simulating pipe organ tones by means of an electric organ, comprising a. division of said electric organ, means connected to said division for dividing its tonal output into separate channels on a frequency divi sion basis, means for introducing exponential build-up of tone into at least one of said channels, build-up time being in accordance with the build-up time of corresponding frequencies of said pipe organ, and acoustic radiating means connected to said channel-s and arranged to radiate into a common acoustic space, said channels including an infrasonic channel, and a separate infrasonic loudspeaker connected to said infrasonic channel.

17. The combination according to claim 16 wherein only one of said channels conveys the infrasonic output of said division, said infrasonic loudspeaker being connected to said only one of said channels.

18. In an electronic organ, a source of harmonic-rich tone of a given single nomenclature, a frequency range dividing network in cascade with said source and having plural channel outputs of relatively low frequencies and relatively high frequencies, means for relatively delaying said relatively low frequencies with respect to said relatively high frequencies, means for recombining the relatively delayed relatively low frequencies and the relatively high frequencies, and means for acoustically radiating the recombined tone.

19. In an electric organ, a plurality of complex tone generators of different nomenclature, a separate frequency range dividing network in cascade with each of said tone generators, each of said frequency range dividing networks providing at least a low frequency output channel and a high frequency output channel, separate exponential delay devices included in each of the low frequency output channels, means for linearly mixing outputs of said channels, acoustic radiating means connected to said means for linearly mixing, and means for separately keying on said tone generators at will, said separate exponen tial delay devices introducing delay times selected to simulate pipe organ delay times for pipes corresponding with References Cited UNITED STATES PATENTS 2,489,497 11/1949 Oswald 841.19 2,539,826 1/1951 George 841.19 X 2,782,307 2/1957 Von Sivers et a1. 307-885 2,793,554 5/1957 Foust 84-.126 3,052,851 9/1962 Heberling 307-885 OTHER REFERENCES Proposed Keyboard Musical Instrument, The Journal of the Acoustical Society of America, Clark, April 1959, pp. 403-419.

ARTHUR GAUSS, Primary Examiner.

GEORGE N. WESTBY, Examiner. E. DREYFUS,'D, D. FORRER, Assistant Examiners. 

8. THE METHOD OF SIMULATING PIPE ORGAN TONES ELECTRONICALLY, WHICH INCLUDES THE STEPS OF: KEYING THE ELECTRICAL OUTPUT OF AUDIO-FREQUENCY SIGNAL GENERATORS, APPLYING THE KEYED SIGNALS TO THE INPUTS OF BOTH A CONTROL CIRCUIT AND A VARIABLE AMPLIFICATION CIRCUIT, DERIVING FROM THE CONTROL CIRCUIT RESULTING CONTROL VOLTAGE GRADUALLY CHANGING IN TIME TO A NEW FIXED VALUE, APPLYING THE CONTROL VOLTAGE TO THE VARIABLE AMPLIFICATION CIRCUIT TO INCREASE ITS GAIN GRADUALLY TO A NEW FIXED VALUE, THUS SIMULATING THE DELAYED BUILD UP OF TONES FROM ORGAN PIPES. 